The present invention relates in general to forming a layer of hardfacing material having coated or encrusted ceramic particles such as cubic boron nitride particles dispersed within a matrix deposit and, more particularly, to an improved hardfacing having enhanced wear resistance properties when deposited on steel alloy surfaces and other generally metallic substrates.
Hardfacing of metal surfaces and substrates is a well known technique to minimize or prevent erosion and abrasion of the metal surface or substrate. Hardfacing can be generally defined as applying a layer of hard, abrasion resistant material to a less resistant surface or substrate by plating, welding, spraying or other well known deposition techniques. Hardfacing is frequently used to extend the service life of drill bits and other downhole tools used in the oil and gas industry. Tungsten carbide and its various alloys are some of the more widely used hardfacing materials to protect drill bits and other downhole tools associated with drilling and producing oil and gas wells.
Hardfacing is typically a mixture of a hard, wear-resistant material embedded in a matrix deposit which is preferably fused with the surface of a substrate by forming metallurgical type bonds to ensure uniform adherence of the hardfacing to the substrate. For some applications, wear-resistant material such as an alloy of tungsten carbide and/or cobalt is placed in a steel tube which serves as a welding rod during welding of the hardfacing with the substrate. This technique of applying hardfacing is sometimes referred to as xe2x80x9ctube rod welding.xe2x80x9d Tungsten carbide/cobalt hardfacing applied with tube rods has been highly successful in extending the service life of drill bits and other downhole tools.
Rotary cone drill bits are often used for drilling boreholes for the exploration and production of oil and gas. This type of bit typically employs three rolling cone cutters, also known as rotary cone cutters, rotatably mounted on spindles extending from support arms of the bit. The cutters are mounted on respective spindles that typically extend downwardly and inwardly with respect to the bit axis so that the conical sides of the cutters tend to roll on the bottom of a borehole and contact the formation.
For some applications, milled teeth are formed on the cutters to cut and gouge in those areas that engage the bottom and peripheral wall of the borehole during the drilling operation. The service life of milled teeth may be improved by the addition of tungsten carbide particles to hard metal deposits on selected wear areas of the milled teeth. This operation is sometimes referred to as xe2x80x9chardfacing.xe2x80x9d U.S. Pat. No. 4,262,761, issued Apr. 21, 1981 discloses the application of hardfacing to milled teeth and is incorporated by reference for all purposes within this application.
For other applications, sockets may be formed in the exterior of the cutters and hard metal inserts placed in the sockets to cut and gouge in those areas that engage the bottom and peripheral wall of the borehole during the drilling operation. The service life of such inserts and cutters may be improved by carburizing the exterior surface of the cutters. U.S. Pat. No. 4,679,640 issued on Jul. 14, 1987 discloses one procedure for carburizing cutters and is incorporated by reference for all purposes within this application.
A wide variety of hardfacing materials have been satisfactorily used on drill bits and other downhole tools. A frequently used hardfacing includes sintered tungsten carbide particles in an alloy steel matrix deposit. Other forms of tungsten carbide particles may include grains of monotungsten carbide, ditungsten carbide and/or macrocrystalline tungsten carbide. Satisfactory binders may include materials such as cobalt, iron, nickel, alloys of iron and other metallic alloys. For some applications loose hardfacing material is generally placed in a hollow tube or welding rod and applied to the substrate using conventional welding techniques. As a result of the welding process, a matrix deposit including both steel alloy melted from the substrate surface and steel alloy provided by the welding rod or hollow tube is formed with the hardfacing. Various alloys of cobalt, nickel and/or steel may be used as part of the binder for the matrix deposit. Other heavy metal carbides and nitrides, in addition to tungsten carbide, have been used to form hardfacing.
Both natural and synthetic diamonds have been used in downhole drill bits to provide cutting surfaces and wear-resistant surfaces. U.S. Pat. No. 4,140,189 teaches the use of diamond inserts protruding from the shirttail surface of a roller cone bit. Polycrystalline diamond (PCD) gauge inserts are frequently used on a wide variety of drill bits to prevent erosion and wear associated with harsh downhole drilling conditions. U.S. Pat. No. 4,140,189 is incorporated by reference for all purposes within this application.
Accordingly, a need has arisen in the art for an improved hardfacing material. The present invention provides a hardfacing material that substantially eliminates or reduces problems associated with prior hardfacing materials.
In accordance with the present invention, a hardfacing material may comprise coated ceramic particles and/or other coated particles of superabrasive and superhard materials which may be metallurgically bonded with a deposit matrix to form the desired hardfacing. The coated particles are also mechanically held in place and protected by the surrounding matrix deposit which is preferably also formed from hard materials. Ceramic particles and other superabrasive or superhard particles satisfactory for use with the present invention may be commonly found as phases in the boron-carbon-nitrogen-silicon family of alloys and compounds. Examples of hard particles satisfactory for use with the present invention include silicon nitride (Si3N4), silicon carbide (SiC), boron carbide (B4C) and cubic boron nitride (CBN). The coated particles are preferably dispersed within and both metallurgically and mechanically bonded with a deposit matrix formed from hard materials which are wear resistant. Cooperation between the wear resistance deposit matrix and the coated particles provides an enhanced hardfacing to better withstand abrasion, wear, erosion, and other stresses.
One aspect of the present invention includes providing hardfacing with coated ceramic particles and other types of coated particles formed in part from superabrasive and superhard materials with the coated particles dispersed throughout the hardfacing. Another aspect of the present invention includes providing a drill bit with layers of hardfacing having coated or encrusted cubic boron nitride particles disposed therein. The resulting hardfacing is able to better withstand abrasion, wear, erosion and other stresses associated with repeated use in a harsh, downhole drilling environment.
Technical advantages of the present invention include providing a layer of hardfacing material on selected portions of a drill bit to prevent undesired wear, abrasion and/or erosion of the protected portions of the drill bit. For one application, a layer of hardfacing having coated or encrusted cubic boron nitride particles may be deposited on selected exterior surfaces of milled teeth to prevent premature wear of the milled teeth during downhole drilling and to substantially extend the life of the associated drill bit.
Further aspects of the present invention include mixing coated or encrusted cubic boron nitride particles with conventional tube rod compositions to provide an enhanced hardfacing surface on a substrate. For one embodiment of the present invention, each milled tooth on a rotary cone drill bit is completely covered with a layer. of hardfacing material which includes coated or encrusted cubic boron nitride particles in accordance with the teachings of the present invention. The coated or encrusted cubic boron nitride particles are preferably sintered prior to mixing with the other materials which will be used to form the layer of hardfacing on the substrate.
Technical advantages of the present invention include coating or encrusting ceramic particles such as cubic boron nitride particles or hard particles formed from other superabrasive and superhard materials and sintering the coating to form chemical or metallurgical bonds between the coating and the surface of the associate ceramic particle or other hard particle. Varying the composition of the coating and/or sintering the coating can also be used to vary the density of the resulting coated particles to be equal to or greater than the density of the hard materials used to form the associated matrix deposit when the matrix deposit is in its molten state prior to solidification. The coating on the hard particles can also be reinforced with small grains of boride, carbide, oxide and/or nitride which cooperate with other components of the matrix deposit to improve retention of the coated particles within the matrix deposit during erosion, abrasion and/or wear of the associated hardfacing.
The hard materials which will form the resulting matrix deposit and coated particles disposed therein are preferably applied to a substrate by hardfacing techniques which form chemical or metallurgical bonds between the surface of the substrate and the resulting matrix deposit, and between the matrix deposit and the coating on each particle. Both the matrix deposit and the coating can be formed from a wide variety of metallic and ceramic compounds in accordance with teachings of the present invention.
Further technical advantages of the present invention include coating or encrusting cubic boron nitride particles which will protect the associated cubic boron nitride particles from decomposition through exposure to high temperatures associated with various hardfacing techniques. For some applications, each cubic boron nitride particle is preferably encrusted with a coating having a thickness which is roughly equal to one half the diameter of the respective cubic boron nitride particle. As a result of the teachings of the present invention, the extreme hardness of cubic boron nitride particles and other ceramic particles or particles of superabrasive and superhard materials can be integrated into a slightly less hard but much tougher matrix deposit formed from materials such as tungsten carbide. The abrasion, erosion and wear resistance of the hard particles is augmented by the hard materials selected to form the respective coating for each hard particle. For example, when the hard materials selected to form the coating include cobalt, the tougher cementing phase of metallic cobalt will substantially improve the abrasion, erosion and wear resistance associated with cubic boron nitride particles.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims.